Piezoelectric vibration device

ABSTRACT

A piezoelectric vibration device utilizes a thickness-shear vibration available for communication devices or the like. The piezoelectric vibration device has a structure wherein at least one of each peripheral zone of an input electrode ( 21 ) and an output electrode ( 22 ), or a common electrode ( 23 ), where the non-harmonic overtone mode is relatively strongly excited, is partially provided with either a weight reducing portion ( 231, 232 ) or a weight adding portion. Moreover, an area of the common electrode ( 23 ) is larger than a total area of the input electrode ( 21 ) and the output electrode ( 22 ), and either the weight reducing portion ( 231, 232 ) or the weight adding portion reaches the common electrode ( 23 ) opposed to the input electrode ( 21 ) and the output electrode ( 22 ). Preferably, the common electrode formed on one principal plane of a quartz plate ( 1 ) is twice to 10 times as thick as the input electrode ( 21 ) and the output electrode ( 22 ) formed on the other principal plane. As an electrode material, any of gold, silver, or a metal material mainly composed of gold or silver is employed, whereby the spurious vibration mode generated near the principal vibration is restrained, the pass band characteristics are excellent and wider, and the guarantee attenuation characteristics in the portions outside of the pass band are enhanced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric vibration deviceutilizing a thickness-shear vibration available for communicationdevices or the like. In giving particulars, the present inventionrelates to a piezoelectric vibration device which can restraininfluences by a spurious vibration or an unnecessary vibration of thegeneral non-harmonic overtone mode, and enhance guarantee attenuationcharacteristics.

2. Description of the Prior Art

Referring to FIGS. 31 and 32, prior art is described as below.

FIG. 31 is a diagram of an electrode structure and a vibrational energydistribution of spurious vibration of non-harmonic overtone mode,generally referred to as a (3,1,3) mode, seen from a bottom surface of aconventional piezoelectric vibration device. FIG. 32 is a sectional viewalong line S—S in FIG. 31 and a diagram of the vibrational energydistribution of spurious vibration of a principal vibration mode(substantial line) and the (3,1,3) mode. Each symbol of (3,1,3)designates an order of overtone in a Y′-axis (thickness) direction, anorder of overtone in an X′-axis direction, and an order of overtone in aZ′-axis direction. As shown in FIG. 31, the (3,1,3) mode is a mode ofthe spurious vibration having three vibration crests (troughs) arrangedin parallel to the Z′-axis direction.

As a quartz plate 90, an AT cut quartz plate is employed. A principalplane of the quartz plate 90 is provided with an input electrode 191, anoutput electrode 192, outgoing electrodes 191 a, 192 a for leading theinput electrode 191 and the output electrode 192 to peripheral portionof the quartz plate 90, and the other principal plane of the quartzplate 90 is provided with a common electrode 193, and an outgoingelectrode 193a for leading the common electrode 193 to the peripheralportion of the quartz plate 90. Each electrode is formed by means ofthin film forming means using vacuum evaporation method or the like.Though it is not shown, the input and output electrodes 191, 192 arerespectively connected to an input terminal and an output terminal, thecommon electrode 193 is hermetically confined in a state of beingconnected to a grounding terminal.

In the piezoelectric vibration device having such a structure, the inputand output electrodes 191, 192 formed oppositely each other in a statewherein the quartz plate 90 intervenes therebetween and the commonelectrode 193 are designated as resonant areas, a symmetrical mode (fs)and oblique symmetrical mode vibration (fa) are confined by theelectrodes, they are acoustically coupled thereby forming a multiplemode principal vibration with the result that the piezoelectricvibration device having pass band characteristics as a predeterminedfilter is designed.

Moreover, in the prior art, as high-frequency type or three-orderovertone type electrode materials, aluminium is generally employed.

As mentioned above, the piezoelectric vibration device is designed sothat, as well as the principal vibration, a higher-order non-harmonicovertone mode such as the spurious vibration of the (3,1,3) mode isconfined by the electrodes, thus exciting them simultaneously.Furthermore, as well: as such a mode, there are various spuriousvibrations such as one referred as to a (3,3,1) mode having three crests(or troughs) of vibration arranged in parallel in the X-axis direction,or a vibration mode having three crests (or troughs) of vibrationrespectively in the axis direction. These spurious vibrations whereinenergy is confined under exciting electrodes, thus exciting thevibration as a standing wave relatively strongly, have problems whereinspurious vibrations affect the principal vibration, the spuriousvibrations disorders the pass band characteristics, and the guaranteeattenuation characteristics in portions outside of the pass band are notobtained enough. In case of employing aluminium as the electrodematerial in the same way as prior art, it is easy to oxidize aluminium,thus resulting in bad yield and productivity. In addition, in case thataluminium oxide is formed by oxidizing aluminium, a conductiveresistance to a conductive adhesive is greater so that the guaranteeattenuation characteristics are inferior.

SUMMARY OF THE INVENTION

In order to solve the problems, an object of the present invention is toprovide a piezoelectric vibration device for restraining the spuriousvibration mode generated near the principal vibration (what is called“frequency”), making the pass band characteristics more excellent andwider, and enhancing the guarantee attenuation characteristics in theportions outside of the pass band.

In order to achieve the object of the present invention, a piezoelectricvibration device utilizing a thickness-shear vibration having a resonantarea formed by an input electrode, an output electrode and a commonelectrode, the piezoelectric vibration device comprises a quartz platehaving a pair of principal planes, the input electrode and the outputelectrode disposed on a principal plane of the quartz plate, the inputelectrode and the output electrode formed close to each other at aregular interval, and the common electrode disposed on the otherprincipal plane of the quartz plate, corresponding to the inputelectrode and the output electrode, wherein either a weight reducingportion or a weight adding portion is partially disposed on at least oneof each peripheral zone of the input electrode, the output electrode andthe common electrode.

In a three-pole-type piezoelectric vibration device utilizing athickness-shear vibration having a resonant area formed by an inputelectrode, an output electrode, a grounding electrode and a commonelectrode, the piezoelectric vibration device comprising a quartz platehaving a pair of principal planes, the input electrode and the outputelectrode disposed on a principal plane of the quartz plate, thegrounding electrode interposed between the electrodes, in which theinput electrode, the output electrode and the grounding electrode areformed close to each other at regular intervals, and the commonelectrode disposed on the other principal plane of the quartz plate,corresponding to the input electrode, the output electrode, and thegrounding electrode, and in a four-pole-type piezoelectric vibrationdevice utilizing a thickness-shear vibration having resonant areasformed by two pairs of input and output electrodes and commonelectrodes, the piezoelectric vibration device comprising a quartz platehaving a pair of principal planes, the two pairs of input and outputelectrodes respectively including an input electrode and an outputelectrode, disposed on a principal plane of the quartz plate inparallel, in which the input electrode and the output electrode areformed close to each other at a regular interval, and the commonelectrodes disposed on the other principal plane of the quartz plate,corresponding to the respective pairs of input and output electrodes,the weight reducing portion or the weight adding portion is applicable.

Preferably, either the weight reducing portion or the weight addingportion is disposed on a portion where a vibrational energy of aspurious vibration generated in excitation of the piezoelectricvibration device is relatively greater than that of a principalvibration.

In addition, the piezoelectric vibration device comprises a quartz platehaving a pair of principal planes, a rectangular input electrode and arectangular output electrode disposed on a principal plane of the quartzplate, the input electrode and the output electrode formed close to eachother at a regular interval, a rectangular common electrode disposed onthe other principal plane of the quartz plate, corresponding to theinput electrode and the output electrode, and a resonant area formed bythe input electrode, the output electrode and the common electrode, inwhich the piezoelectric vibration device utilizing a thickness-shearvibration includes an outgoing electrode for leading the each electrodeto peripheral ends of the quartz plate, and either the weight reducingportion or the weight adding port-ion is disposed on at least one centerof far sides where the input electrode and the output electrode areopposite to each other, at least one center of far sides opposite to thecommon electrode, or at least one center of the far sides where theinput electrode and the output electrode are opposite to each other aswell as at least one center of the far sides opposite to the commonelectrode.

In the piezoelectric vibration device, the weight reducing portion maybe provided with a notch, and designed by a concave portion formed byremoving a whole or a part of the electrode corresponding to eachpredetermined portion of the electrodes.

Moreover, the weight adding portion may be designed so that a part or awhole of the electrode may be formed thickly or so that resin materialsmay be partially or wholly added to the electrode.

Furthermore, an area of the common electrode is formed to be larger thana total area of the input electrode and the output electrode, and theperipheral zone of the common electrode is at least partially providedwith either the weight reducing portion or the weight adding portionwhich reaches the common electrode opposite to the input electrode andthe output electrode.

In the piezoelectric vibration device according to the presentinvention, the electrode formed on one principal plane of the quartzplate may be thickly formed structurally.

Preferably, in the piezoelectric vibration device, the common electrodeformed on one principal plane of the quartz plate is twice to 10 timesas thick as the input electrode and the output electrode formed on theother principal plane.

In the piezoelectric vibration device according to the presentinvention, preferably, the electrode formed on one principal plane ofthe quartz plate is made of a metal material mainly composed of gold orsilver, gold or silver.

As shown in FIG. 10, in the spurious vibration of the non-harmonicovertone mode, it is well known that the vibration energy distributionis inclined rather more outwardly than the principal vibration modegenerated by coupling a symmetrical mode vibration (fs) and an obliquesymmetrical mode vibration (fa) acoustically, and in the peripheral zoneof the common electrode which is opposed to the input electrode and theoutput electrode, the vibration energy of the spurious vibration ishigher than that of the principal vibration. Herein, according to thepresent invention, the peripheral zone of the common electrode isprovided with the weight reducing portion or the weight adding portion,as it is obvious from the vibration energy distribution as shown in FIG.1, a balance of the spurious vibration is extremely lost, thus weakeningthe vibration energy of the spurious vibration as a whole.

Also, in the three-pole-type or the four-pole-type piezoelectricvibration device, the spurious vibration can be shifted, thus weakeningthe vibration energy in the same way.

Moreover, by a structure of the weight reducing portion or the weightadding portion, the principal vibration mode is concentrated on a centerof an exciting electrode with the result that the acoustic couplebetween the symmetrical mode vibration (fs) and the oblique symmetricalmode vibration (fa) is reinforced to extend the width of the pass bandin the piezoelectric vibration device.

Moreover, an area of the common electrode is larger than the total areaof the input electrode and the output electrode opposite thereto,whereby, for example, the non-harmonic overtone mode is inclined moreoutwardly than the energy distribution of the vibration. In such astate, the periphery of the common electrode is at least partiallyprovided with either the weight reducing portion or the weight addingportion, which structurally reaches the common electrode oppositethereto, so that the non-harmonic overtone mode itself loses thebalance, thus damping the vibration energy much efficiently. Though,generally, the electrode area is larger, thereby making it possible tolower a driving -impedance, various kinds of spurious vibrations aresimultaneously reinforced. On the other hand, according to the presentinvention, the weight reducing portion or the weight adding portion isprovided whereby the spurious vibration can be weakened to a leveladapted for practical use.

The piezoelectric vibration device has a structure wherein the electrodeformed on either principal plane of the quartz plate is thickly formed,whereby a boundary condition formed by the peripheral end surface of theexciting electrode is further emphasized to produce efficiently aneffect obtained by disposing the weight reducing portion or the weightadding portion, thus enhancing an effect on the spurious restriction.

Preferably, the common electrode formed on one principal plane of thequartz plate is twice to 10 times as thick as the input electrode andthe output electrode formed on the other principal plane, in order torelease the energy of the spurious vibration outwardly, and a boundarycondition formed by the peripheral end surface of the exciting electrodeis much emphasized, which makes it possible to produce an effectobtained by disposing the weight reducing portion or the weight addingportion, thus enhancing an effect on the spurious restriction and theguarantee attenuation characteristics.

In case that-the electrode is made of a metal material mainly composedof gold or silver, and the spurious vibration is a thickness-shearnon-harmonic vibration as mentioned above, owing to the electrodestructure made of the metal whose relative density is greater, thedecrease amount of frequency of the non-harmonic vibration is smallerthan that of the principal vibration, the spurious vibration isseemingly higher frequency than the principal vibration. That is, thespurious vibration can be far from the principal vibration. In addition,it is not easier to oxidize silver than aluminium, there is nopossibility wherein the conductive resistance to the conductive adhesiveis not increased, thus enhancing the attenuation characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a principal plane having a commonelectrode in a first embodiment of a monolithic crystal filter of apreferable piezoelectric vibration device according to the presentinvention.

FIG. 2 is a sectional view along A—A line in FIG. 1.

FIG. 3 is a sectional view along B—B line in FIG. 1.

FIG. 4 is a plan view showing a principal plane having a commonelectrode in a second embodiment according to the present invention.

FIG. 5 is a plan view showing a principal plane having a commonelectrode in a third embodiment according to the present invention.

FIG. 6 is a sectional view along C—C line in FIG. 5.

FIG. 7 is a sectional view showing a fourth embodiment according to thepresent invention.

FIG. 8 is a plan view showing a principal plane having a commonelectrode in a fifth embodiment according to the present invention.

FIG. 9 is a sectional view along D—D line in FIG. 8.

FIG. 10 is a sectional view along E—E line in FIG. 8.

FIG. 11 is a diagram showing a thickness of each electrode, applicablefor each embodiment according to the present invention.

FIG. 12 is a graph showing a frequency characteristic of the firstembodiment as shown in FIG. 1.

FIG. 13 is a graph showing a frequency characteristic of the;fifthembodiment as shown in FIG. 8.

FIG. 14 is a plan view showing a principal plane having a commonelectrode in a modification of the fifth embodiment according to thepresent invention.

FIG. 15 is a graph showing a frequency characteristic of a modificationof the fifth embodiment as shown in FIG. 14.

FIG. 16 is a plan view showing a principal plane having a commonelectrode in a sixth embodiment according to the present invention.

FIG. 17 is a graph showing a frequency characteristic of the sixthembodiment as shown in FIG. 16.

FIG. 18 is a plan view showing a principal plane having a commonelectrode in a modification of the sixth embodiment according to thepresent invention.

FIG. 19 is a graph showing a frequency characteristic in a modificationof the sixth embodiment as shown in FIG. 18.

FIG. 20 is a plan view showing a principal plane having a commonelectrode in another modification of the sixth embodiment according tothe present invention.

FIG. 21 is a plan view of a principal plane having a common electrode,for illustrating an electrode structure of a piezoelectric vibrationdevice employable for obtaining the frequency characteristic generatedby an electrode material.

FIG. 22 is a graph showing a frequency characteristic under a conditionwherein the electrode material is aluminium in the electrode structureas shown in FIG. 21.

FIG. 23 is a graph showing a frequency characteristic under a conditionwherein the electrode material is silver in the electrode structure asshown in FIG. 21.

FIG. 24 is a graph showing a guarantee attenuation characteristic to thethickness of the common electrode under a condition wherein theelectrode material is a multiple-layer structure ofchrome-silver-chrome, a thickness of a split electrode is 500 Å, and aprincipal vibration frequency is 130 MHz.

FIG. 25 is a graph showing an insertion loss characteristic to thethickness of the common electrode under a condition wherein theelectrode material is the multiple-layer structure ofchrome-silver-chrome, the thickness of a split electrode is 500 Å, andthe principal vibration frequency is 130 MHz.

FIG. 26 is a graph showing a guarantee attenuation characteristic to thethickness of the common electrode under a condition wherein theelectrode material is the multiple-layer structure ofchrome-silver-chrome, the thickness of the split electrode is 500 Å, andthe principal vibration frequency is 45 MHz.

FIG. 27 is a graph showing an insertion loss characteristic to thethickness of the common electrode under a condition wherein theelectrode material is the multiple-layer structure ofchrome-silver-chrome, the thickness of the split electrode is 500 Å, andthe principal vibration frequency is 45 MHz.

FIG. 28 is a plan view showing a principal plane having a commonelectrode in a seventh embodiment according to the present invention.

FIG. 29 is a plan view showing a principal plane having a commonelectrode in an eighth embodiment according to the present invention.

FIG. 30 is an exploded perspective view of a package employed for ameasurement of a frequency characteristic of the piezoelectric vibrationdevice.

FIG. 31 is a plan view showing a principal plane having a commonelectrode of a conventional piezoelectric vibration device.

FIG. 32 is a sectional view along S—S line in FIG. 31.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, preferred embodiments of the inventionare described in detail below.

FIG. 1, FIG. 2 and FIG. 3 are explanatory diagrams of a first embodimentaccording to the present invention, employing a monolithic crystalfilter. FIG. 1 is a plan view of a principal plane having a commonelectrode. FIG. 2 is a sectional view along line A—A in FIG. 1. FIG. 3is a sectional view along line B—B in FIG. 1. FIG. 1 and FIG. 3illustrate typically a vibration energy distribution state of aprincipal vibration mode and a vibration energy of (3,1,3) mode, i.e.,one of the spurious vibration.

As the quartz plate 1, an AT cut quartz plate is employed, which isworked rectangularly. On one principal plate (bottom surface) of thequartz plate 1, a pair of a rectangular input electrode 21 and arectangular output electrode 22 are formed close to each other, at apredetermined interval in a Z′-axis direction. The input electrode 21and the output electrode 22 are led to each corner positioned on adiagonal line of the quartz plate 1 by the outgoing electrodes 21 a, 22a. Moreover, on the other principal plane (upper surface), opposite tothe input electrode 21 and output electrode 22, a rectangular commonelectrode 23 is formed, the common electrode 23 is led to the othercorner of the quartz plate 1 by the outgoing electrode 23 a, toconnected to a grounding terminal (not shown). A central portion of ashorter side of the common electrode 23 is provided with notches 231,232. As illustrated obviously in sectional views in FIGS. 2 and 3, thepositions of the peripheral ends of the input electrode 21, the outputelectrode 22 and the common electrode 23 are predetermined at theapproximately same position as the other principal plane each other(upper and bottom surface), and notches 231, 232 of the common electrode23 are scooped inwardly.

In case of exciting the monolithic crystal filter having the abovestructure, it shows a frequency characteristic shown in FIG. 12.Compared with FIG. 22 showing the frequency characteristic of themonolithic crystal filter in prior art, in the embodiment according tothe present embodiment, a spurious vibration such as a non-harmonicovertone mode having a relative great vibration energy conventionally isdamped. This is owing to characteristic electrode structure in thepresent embodiment, an electric field is not added to notches 231, 232,whereby it seems to be the reason that exciting according to counterpiezoelectric effect is not performed. In other words, it is thoughtthat, according to the vibration energy distribution, as shown in FIG.1, the vibration loses the balance along the notches 231, 232, thevibration energy of the non-harmonic overtone mode as shown in FIG. 3 isrestricted to be weakened. Moreover, the pass band of the presentinvention is wider than that of the prior art though it is hard torecognize it in FIG. 12.

The monolithic crystal filter employed for the present invention is arectangular shaped AT cut quartz plate, being 2.5 mm by 5, having acenter frequency thereof predetermined at 130 MHz, wherein a pair ofrectangular electrodes having longer sides of 0.78 mm, shorter sides of0.56 mm are formed on the back side at an interval of 0.1 mm between theelectrodes, and a common electrode opposite to the pair of the input andoutput electrodes, having a size almost correspond thereto is formed onthe surface. Therefore, the common electrode of the present inventionhas a different shape from that of the prior art. As a shape ofelectrode for reducing the weight, for example, notches formed on thecommon electrode are illustrated according to the present embodiment. Ashape of the notch is not limited to the shape illustrated in thepresent embodiment, and a shape and a size which do not have influenceon displacement distribution of the principal vibration mode areallowed, including a curve shape.

The monolithic crystal filter has structures not shown, in other words,one structure wherein a base having lead terminals respectivelyconnected to a supporting body is prepared, and the quartz plate 1 ofthe above electrode structure may be supported by the supporting bodyconnected to the lead terminals to be hermetic by a cap, and anotherstructure wherein the quartz plate may be mounted on a package having anouter leading electrode pad thereby being hermetic.

As a shape of the electrode for reducing the weight, a secondembodiment, or a structure wherein electrode portions in predeterminedportions of the electrode are removed to form a piercing hole, isdescribed below.

FIG. 4 is a plan view of a back surface where a common electrode isformed so as to illustrate the structure of the second embodiment. Thesame elements as those in the first embodiment are allocated to the samereferences and the description thereof is omitted.

In this embodiment, a common electrode 24 is led to each cornerpositioned on a diagonal line on the quartz plate 1 by outgoingelectrodes 24 a, 24 b.

The common electrode 24 formed on the back surface of the quartz plate 1is provided with a number of pits 241, 242, 243, 244, 245, 246, theportions where these pits are formed are areas where the spuriousvibration of the (3,3,1) mode is relatively strongly excited. The eachpit can be formed by well-known means such as removing the electricmaterial of the predetermined portions by emitting laser beams afterforming the exciting electrodes. By such an arrangement, it is thoughtthat the spurious vibration of the (3,3,1) mode loses the balance todamp the vibration energy.

Though the second embodiment has a structure wherein the piercing holeis formed on the common electrode, the structure is not limited to thepiercing hole, the structure wherein a part of the electrode is madethinly to form the pit (concave), is allowed. Moreover, the structurewherein these piercing holes and pits are mixed with the mentioned-abovenotches may be allowed.

Furthermore, as an electrode shape for reducing the weight, a thirdembodiment for illustrating a structure wherein the electrode as shownin FIGS. 5 and 6 is formed is described as below.

FIG. 5 showing a structure of the third embodiment is a plan view of theback surface where the common electrode is formed. FIG. 6 is a sectionalview along C—C line in FIG. 5. The same elements as those in the firstembodiment are allocated to the same numerals and the descriptionthereof is omitted.

On one principal plane, an input electrode 31 and an output electrode 32are formed in parallel to a Z′-axis direction, at a predeterminedinterval therebetween, close to each other. The input electrode 31 andthe output electrode 32 are led to each corner positioned on eachdiagonal line on the quartz plate 1 by outgoing electrodes 31 a, 32 a.On the other principal plane, common electrodes 33 and 34 are formedopposite to the input electrode 31 and the output electrode 32. Thesecommon electrodes 33, 34 are led to each corner positioned on eachdiagonal line on the quartz plate 1 by outgoing electrodes 33a, 34a.Moreover, each electrode has an arrangement wherein a pair of the inputelectrode 31 and the output electrode 32, and a pair of the commonelectrodes 33, 34 have far sides being arc shaped, opposite to eachother in an X-axis direction. By the arrangement, a shape thereof ispartially similar to the oval vibration energy distribution, thus makingit possible to adopt it. Though the embodiment employs an arrangementwherein the electrodes are arranged in parallel to the X-axis direction,it is an optional matter selected depending on desired electriccharacteristics such as a necessity for extending the pass band.

The third embodiment, in order to reduce the weight, has an arrangementwherein a notch 331 is formed at a center of the circular arc shaped endof the common electrode 33 and a notch 321 is formed at a center of thecircular arc shaped end of the output electrode 32. The arrangementwherein those notches are formed, in the same way as the first andsecond embodiments, can make the vibration energy of the spuriousvibration of: the non-harmonic overtone mode or the like be damped.

A fourth embodiment is described as below, referring to FIG. 7 of asectional view of a monolithic crystal filter having a shape of anelectrode to which a weight is added.

In the same electrode structure of the present invention as that of theprior art in FIG. 31, an additional electrode 371 made of the samematerial as that of a common electrode 37 is formed at one end of theelectrode 37. The forming portion of the additional electrode 371 is aportion where the non-harmonic overtone mode is relatively stronglyexcited, thereby damping the spurious vibration of the non-harmonicovertone mode or the like.

A fifth embodiment is described as below, referring to FIGS. 8 to 10.

FIG. 8 is a plan view of the principal plane on the common electrodeside. FIG. 9 is a sectional view along D—D line in FIG. 8. FIG. 10 is asectional view along E—E line in FIG. 8.

According to the embodiment, a rectangular common electrode 43 formed onone principal plane has four sides being longer than those of arectangular input electrode 41 and a rectangular output electrode 42formed on the other principal plane, so as to cover the both of theinput electrode 41 and the output electrode 42. Notches 431, 432 areformed at the each center of shorter sides opposite to the commonelectrode 43. The depth of the notches reaches the common electrode 43opposite to the input and output electrodes 41, 42 formed on the backside.

The common electrode 43 is led to another corner of the quartz plate 1by an outgoing electrode 43 a, to be connected to a grounding terminal(not shown). Moreover, the input electrode 41 and the output electrode42 are led to each corner positioned on a diagonal line on the quartzplate 1 by outgoing electrodes 41 a, 42 a.

By adopting the above mentioned structure, especially the non-harmonicovertone mode loses the balance owing to the vibration energydistribution in a state wherein the non-harmonic overtone mode isinclined much outwardly, thus damping the vibration energy extremelyefficiently. Generally, the electrode area is increased, thus making itpossible to lower the driving impedance, on the other hand, causing aproblem wherein various kinds of the spurious vibrations are strongersimultaneously. However, by employing a structure of the electrode shapefor reducing the weight, or a structure of the electrode shape foradding the weight, the spurious vibration can be weakened to a practicaluse level.

In a structure shown in FIG. 8, notches are positioned in a Z′-axisdirection so as to face opposite to each other. However, positionsthereof are not limited to the Z′-axis direction, notches 931, 932, 933,934 may be structurally formed in an X-axis direction on a commonelectrode 93 as shown in FIG. 20. In case that the structure as shown inFIG. 20 wherein the common electrode has shorter sides L₀ of 1.30 mm,and the input and output electrodes have each width L₂ of 0.78 mm, arelation between an X-axis directional distance L₁ from one notch to theother disposed in the X-axis direction so as to be opposite to eachother, and a spurious damping amount is illustrated in Table 1.

TABLE 1 Spurious Damping L1 (mm) Amount (dB) 1.30 3 0.59 12 0.54 13 0.4915

As it is obvious from the above table, with L₁ is less, in other words,the depth of the notches is greater, the damping amount of the spuriousvibration is greater, leading to being preferable.

A monolithic crystal filter employed for the fifth embodiment is arectangular shaped AT cut quartz plate, being 2.5 mm by 5, having acenter frequency thereof predetermined at 130 MHz, and has anarrangement wherein a pair of rectangular electrodes having longer sidesof 0.78 mm, shorter sides of 0.56 mm are formed on the back side at aninterval of 0.1 mm between the electrodes, and a rectangular commonelectrode 43 having longer sides of 1.84 mm and shorter sides of 1.1 mmis formed on the surface so as to cover the input and output electrodes.As a frequency characteristic in the monolithic crystal filter of theabove arrangement is shown in FIG. 13, compared with FIG. 22 showing afrequency characteristic in the monolithic crystal filter of the pirorart, it is obvious that the spurious vibration of the non-harmonicovertone mode or the like, having conventionally relatively greatervibration energy, is damped. Also, the above case, in the same way asthe device according to the first embodiment illustrated in FIG. 12, hasa characteristic wherein the pass band width is greater than that of theconventional product though it is difficult to recognize the fact fromFIG. 13.

As a modification of the fifth embodiment, there is a structure shown inFIG. 14. According to the modification, a rectangular common electrode53 formed on one principal plane has four sides being longer than thoseof a rectangular input electrode 51 and a rectangular output electrode52 formed on the other principal plane so as to cover the both of theinput electrode 51 and the output electrode 52, and the depth of theeach notch 531, 532 reaches the common electrode 53 opposite to theinput and output electrodes 51, 52 formed on the back side, whereby thestructure of the modification is equivalent to that shown in FIG. 8 inthe above points, on the other hand, a shape of the each notch in themodification is different from that in FIG. 8. The common electrode 53is led to each corner positioned on each diagonal line of the quartzplate 1 by outgoing electrodes 53 a, 54 a to be connected to a groundingterminal (not shown) Moreover, the input electrode 51 and the outputelectrode 52 are led to each corner positioned on a diagonal line of thequartz plate 1 by outgoing electrodes 51 a, 52 a.

A frequency characteristic of the monolithic crystal filter having thestructure is shown in FIG. 15, compared with FIG. 22 showing a frequencycharacteristic in the monolithic crystal filter of the prior art, in thesame way as the above mentioned structure in FIG. 8, it is obvious thatthe spurious vibration of the non-harmonic overtone mode or the like,having conventionally the relatively greater vibration energy, isdamped, and it is recognized that the spurious vibration in (f1) and(f2) is far from the principal vibration, thus recognizing the fact ofdamping the spurious vibration (f2)

Next, a sixth embodiment is described as below, referring to FIG. 16.FIG. 16 is a plan view of a principal plane having the common electrode.

According to the embodiment, notches 631, 632 formed on an inputelectrode 61, an output electrode 62 and a common electrode 63 so as toface to each other in a Z′-axis direction are structurally equivalent tothose in the modification shown in FIG. 14. On the other hand, it isstructurally characterized in that notches 633, 634, 635, 636 are formedon the common electrode 63 in an X-axis direction. The notches 633 and634, and 635 and 636 are respectively formed so as to face to eachother.

The frequency characteristic of the monolithic crystal filter is shownin FIG. 17. In the same way as FIG. 15 illustrating the frequencycharacteristic by means of the arrangement shown in FIG. 8 mentionedabove, the spurious vibrations in (f3) and (f4) are far from theprincipal vibration and in the sixth embodiment, it is recognized thatnot only the spurious vibration in (f3) but also that in (f4) aredamped.

Moreover, as a modification of the sixth embodiment, structures in FIGS.18 and 19 can be cited. In an arrangement of the FIG. 18, shapes andforming positions of notches 731, 732, 733, 734 formed on a commonelectrode 73 in an X-axis direction are structurally equivalent to thosein FIG. 16. Though shapes of notches 741 and 742 formed in a Z′-axisdirection are different from those in FIG. 16, forming portions thereofare corresponding to those in FIG. 16. Shorter sides opposite to thecommon electrode 73 are formed outwardly in an arc shape. Thearrangement has the same effect as that in FIG. 16.

In an arrangement shown in FIG. 19, a common electrode 83 is providedwith notches 831, 832, 833, 834 which reach the common electrode 83opposite to an input electrode 81 and an output electrode 82, along eachdiagonal line drawn from each corner of the rectangular electrode. Also,the arrangement has the same effect as that in FIG. 16.

In the above mentioned fifth and sixth embodiments, the common electrodemay have a structure wherein only two sides opposite to each other maybe longer than those of the input and output electrodes, or the commonelectrode may be formed on a whole surface of the quartz plate. However,in case of connecting the quartz plate to an electrode pad of a packageby a conductive connection material or the like, there is a possibilityof causing a short circuit between the outgoing electrodes of the inputand output electrodes formed on the other principal plane and theelectrode pad with the result that an electrodeless area must be formedin order to prevent the problem from happening in case of employing thearrangement.

In the each embodiment, either the input electrode and the outputelectrode on one principal plane or the common electrode on the otherprincipal plane may be formed thickly, for example, as shown in FIG. 11,a thickness G1 of the common electrode 37 is greater than a thickness G2of the input electrode 35 or the output electrode 36. Preferably, thethickness G1 is four times thickness G2, in order to emit the spuriousvibration energy outwardly. With the thickness is increased, the band isincreased. However, after an increment reaches a certain limit, thefurther increment fails to increase the band much more. The device mustbe designed, taking the above fact into consideration. By such anarrangement, changes of boundary condition owing to reducing or adding aweight is further emphasized, thus being capable of restraining thespurious vibration.

In the each embodiment mentioned above, preferably, the common electrodeformed on one principal plane of the quartz plate is twice to 10 timesas thick as the input electrode and the output electrode formed on theother principal plane in order to emit the spurious vibration energyoutwardly. For example, as shown in FIG. 11, the thickness of the commonelectrode 37 is approximately twice the thickness G2 of the inputelectrode 35 and the output electrode 36. The limitation of scopebetween twice and 10 times is designed, in consideration of the factwherein the band is increased with the thickness is increased, but,after the increment reaches a certain limit, the further increment failsto increase the band much more. Referring to experimental dataillustrated in FIGS. 24 and 25, it is described as below.

FIG. 24 shows each guarantee attenuation in case that a multiple-layerstructure of chrome-silver-chrome is employed as an electrode material,the thickness of the input electrode and the output electrode is 500Åand the frequency of the principal vibration is 130 MHz, and thethickness of the common electrode is changed as below: that is 500 Å,1000 Å, 2000 Å, 3000 Å, 4000 Å, 5000 Å, 6000 Å, and 7000 Å. FIG. 25 is agraph for illustrating insertion loss to the each thickness of thecommon electrode. Moreover, FIG. 26 shows each guarantee attenuation incase that the multiple-layer structure of chrome-silver-chrome isemployed as an electrode material, the thickness of the input electrodeand the output electrode is 500 Åand the frequency of the principalvibration is 45 MHz, and the thickness of the common electrode ischanged as below: that is 500 Å, 1000 Å, 2000 Å, 3000 Å, 4000 Å, 5000 Å,6000 Å, and 7000 Å. FIG. 27 is a graph for illustrating the insertionloss to the each thickness of the common electrode.

In case that the frequency of the principal vibration is 130 MHz, theinsertion loss tends to be higher as shown in FIG. 25, whereby theinsertion loss less than approximately 3 dB comes within the employablescope. In case that a frequency of the fundamental wave is 45 MHz, theinsertion loss tends to be lower, whereby the insertion loss less thanapproximately 2 dB comes within the employable scope. Furthermore,taking the most appropriate value of the guarantee attenuationcharacteristics into consideration, in the above both cases, the bestrange of the thickness of the common electrode is from 1000 Åto 5000 Å.The above data support the scope of the thickness of the commonelectrode which is experimentally predetermined at twice to tenfold thethickness of the input and output electrodes.

By the structure mentioned above, better guarantee attenuationcharacteristics are obtained, changes of the boundary condition byreducing or adding a weight are more emphasized with the result that thespurious vibration can be effectively restrained.

The spurious restraining effect is different according to a size (anamount) of a weight reducing portion or a weight adding portion so thatthere are some cases wherein the principal vibration mode is damped.Moreover, the notches must be designed, taking a production error informing the electrode, into consideration.

The multiple-layer structure of chrome-silver-chrome is employed as anelectrode material, in the above embodiments. Compared with aconventional case of employing aluminium as the electrode material, itis advantageous that the spurious vibration can be generated fartherfrom the principal vibration. FIGS. 22 and 23 show frequencycharacteristics in case that the structure shown in FIG. 21 is appliedto the electrodes and aluminium and silver are respectively employed asthe electrode material. Though neither the common electrode 13, theinput electrode 11, nor the output electrode 12 has a structure forreducing or adding a weight, which is a characteristic structure of thepresent invention, only differences of action and effect obtained bydifference of the electrode material are described. As shown in FIG. 22,in case of employing an aluminium electrode, the spurious vibrations(f5), (f6) are greatly generated in the peripheral zone of the principalvibration, but on the other hand, in case of employing a silverelectrode, the spurious vibrations (f7), (f8) are generated far from theprincipal vibration. This is grounded on the reasons as below. First, incase that the spurious vibration being a thickness-shear non-harmonicvibration is formed by a heavy electrode in relative density, adecrement of the frequency of the non-harmonic vibration is smaller thanthat of the frequency of the principal vibration, with the result that,seemingly, the frequency of the spurious vibration is higher than thatof the principal vibration. Second, it is owing to the additionalreasons wherein aluminium is liable to oxidize, and it is a moreunstable material compared with silver. Under the above description,employing silver as the electrode material is effective means in view ofrestraining the influences of the spurious vibration. Furthermore,employing gold instead of silver as the electrode material is alsoallowed. In addition, the electrode material is not limited to only goldand silver, and metal multiple structure mainly composed of gold orsilver including three layer structures such as chrome-silver-gold,chrome-silver-chrome, chrome-gold-chrome, nickel-silver-nickel,chrome-silver-nickel or nickel-silver-chrome, and double layerstructures or electrode structures such as chrome-silver, chrome-gold,nickel-silver, nickel-gold or the like. Also in case of employing theseelectrodes, the same effect as obtained in case of employing only silvercan be obtained.

The frequency characteristics shown in FIGS. 12, 13, 15, 17, 22 and 23are measured by means of package 320 illustrated in an explodedperspective view of FIG. 30. The piezoelectric vibration device 300 tobe measured may be any of the devices according to the presentinvention. For example, as shown in FIG. 30, on a plane of apiezoelectric substrate 310, a pair of input and output vibrationelectrodes 311, 312 are formed so as to have a predetermined gap Gintervening therebetween, and on the other plane, a common electrode 313is formed so as to face thereto, the piezoelectric vibration device 300is housed inside a surface-mounting-type package 320.

The package 320 comprises a package body 321 composed of an insulatingmaterial such as ceramics, and a metallic lid 322 for covering an uppersurface opening of the package body 321 via Kovarring (not shown). Thepackage body 321 is provided with two pits 341, 342 respectively opposedto the input vibration electrode 311 and the output vibration electrode312 on the piezoelectric substrate 310 respectively in an assemblingstate, and a partition 343 between the respective pits 341 and 342 isdisposed along the gap G intervening between the pair of input andoutput vibration electrodes 311, 312.

In the piezoelectric vibration device 300, the pair of input and outputvibration electrodes 311 and 312 facing each bottom of pits 341, 432,are supported by the package body 321 in the peripheral zone of the pits341, 342 at three corners of the piezoelectric substrate 310. The pairof input and output vibration electrode 311, 312 and the commonelectrode 313 are respectively led to three corners of the piezoelectricsubstrate 310 by outgoing electrodes respectively corresponding thereto,and the package body 321 is provided with three connecting pads P at thepositions corresponding to the corners in the peripheral zone of thepits 341, 342. The piezoelectric substrate 310 is automatically securedon the connecting pads P in a state wherein the conductive adhesive doesnot prevent the piezoelectric substrate 310 from vibrating at threecorners, at the same time when the pair of input and output vibrationelectrodes 311, 312 and the common electrode 313 are electricallyconnected to the respective connecting pads P. Under such a condition,the measurement is performed.

In the first to the sixth embodiments mentioned as above, though thetwo-pole-type electrode structure has been described, the embodimentsare also applied to the three-pole-type or four-pole-type piezoelectricvibration device, in the same way. The embodiments are described,referring to FIGS. 28 and 29.

FIG. 28 is a plan view of a principal plane having a common electrode ina seventh embodiment, for illustrating a three-pole-type piezoelectricvibration device.

As a quartz plate 1, an AT cut quartz plate to be worked rectangularlyis employed, on one principal plane, a rectangular input electrode 261,a grounding electrode 263, an output electrode 262 are formed atpredetermined intervals in a state wherein the grounding electrode 263intervenes between the input electrode 261 and the output electrode 262.The input electrode 261 and the output electrode 262 are led to eachcorner positioned on a diagonal line of the quartz plate 1 by outgoingelectrodes 261 a, 262 a, and the grounding electrode 263 is led to eachcorner positioned on another diagonal line thereof by outgoingelectrodes (not shown). On the other hand, on the other principal plane,a common electrode 264 is formed opposite to the input electrode 261,the grounding electrode 263 and the output electrode 262, and the commonelectrode 264 is led to each corner positioned on a diagonal line of thequartz plate 1 by outgoing electrodes 264 a, 264 b, to be connected tothe grounding electrode 263 in common. At the periphery of the commonelectrode 264, notches 265 are formed at a depth wherein the notches canreach the input electrode 261 and the output electrode 262 opposedthereto. In the three-pole-type piezoelectric vibration device, thecommon electrode 264 is provided with a weight reducing portion, thuslosing the balance of the spurious vibration and weakening the vibrationenergy of the spurious vibration as a whole.

FIG. 29 is a plan view of a principal plane having a common electrode inan eighth embodiment, for illustrating a four-pole-type piezoelectricvibration device.

As a quartz plate 1, an AT cut quartz plate to be worked rectangularlyis employed, on one principal plane, two pairs of input and outputelectrodes, or a rectangular input electrode 271 and a rectangularoutput electrode 272, a rectangular input electrode 281 and arectangular output electrode 282 are respectively formed atpredetermined intervals. The input electrode 271 and the outputelectrode 272, and the input electrode 281 and the output electrode 282are respectively led to each corner of the quartz plate 1 by outgoingelectrodes 271 a, 272 a, 281 a, and 282 a. On the other hand, on theother principal plane, common electrodes 273, 283 are formedrespectively so as to be opposed to the input electrode 271 and theoutput electrode 272, and the input electrode 281 and the outputelectrode 282, and the common electrodes 273, 283 are led to each cornerpositioned on each diagonal line of the quartz plate 1 by outgoingelectrodes 273 a, 283 a. At the periphery of the common electrodes 273,283, respective notches 274, 284 are formed at each depth wherein theeach notch can reach the input electrode 271 and the output electrode272, and the input electrode 281 and the output electrode 282 opposedthereto. In the four-pole-type piezoelectric vibration device, thecommon electrodes 274, 284 are respectively provided with weightreducing portions, thus losing the balance of the spurious vibration andweakening the vibration energy of the spurious vibration as a whole.

INDUSTRIAL APPLICABILITY

As mentioned above, according to the present invention, thepiezoelectric vibration device utilizing a thickness-shear vibrationavailable for communication devices or the like, is effective as areliable device by making it possible to restrain influences by aspurious vibration, and enhance guarantee attenuation characteristics.

What is claimed is:
 1. A piezoelectric vibration device utilizing a thickness-shear vibration having a resonant area formed by an input electrode, an output electrode and a common electrode, the piezoelectric vibration device comprising: a quartz plate having a pair of principal planes, the input electrode and the output electrode disposed on a principal plane of the quartz plate, the input electrode and the output electrode formed close to each other at a regular interval, the common electrode disposed on the other principal plane of the quartz plate, corresponding to the input electrode and the output electrode, and a weight reducing notch disposed on each of peripheral zones of the input electrode, the output electrode, and the common electrode, and wherein the weight reducing notch is disposed on the peripheral zones where a vibrational energy of a spurious vibration, generated in excitation of the piezoelectric vibration device, is relatively greater than that of a principal vibration.
 2. A piezoelectric vibration device according to claim 1, wherein the each electrode is formed to be rectangular, and the weight reducing notch is disposed on one center of the far sides where the input electrode and the output electrode are opposite to each other as well as one center of the far sides opposite to the common electrode.
 3. A piezoelectric vibration device according to claim 1, wherein an area of the common electrode is formed to be larger than a total area of the input electrode and the output electrode, and the peripheral zone of the common electrode is at least partially provided with the weight reducing notch reaches the common electrode opposite to the input electrode and the output electrode.
 4. A piezoelectric vibration device according to claim 1, wherein the electrode formed on one principal plane of the quartz plate is thickly formed.
 5. A piezoelectric vibration device according to claim 1, wherein the common electrode formed on one principal plane of the quartz plate is twice to 10 times as thick as the input electrode and the output electrode formed on the other principal plane.
 6. A piezoelectric vibration device according to claim 1, wherein the electrode formed on one principal plane of the quartz plate is made of gold, silver or a metal material mainly composed of gold or silver.
 7. A piezoelectric vibration device utilizing a thickness-shear vibration having a resonant area formed by an input electrode, an output electrode, a grounding electrode and a common electrode, the piezoelectric vibration device comprising: a quartz plate having a pair of principal planes, the input electrode and the output electrode disposed on a principal plane of the quartz plate, the grounding electrode interposed between the electrodes, in which the input electrode, the output electrode and the grounding electrode are respectively formed close to each other at regular intervals, the common electrode disposed on the other principal plane of the quartz plate, corresponding to the input electrode, the output electrode, and the grounding electrode, and a weight reducing notch disposed on each of peripheral zones of the input electrode, the output electrode, and the common electrode, and wherein the weight reducing notch is disposed on the peripheral zones where a vibrational energy of a spurious vibration, generated in excitation of the piezoelectric vibration device, is relatively greater than that of a principal vibration.
 8. A piezoelectric vibration device according to claim 7, wherein the weight reducing notch disposed on the electrodes on a principal plane reaches an area opposite and corresponding to the electrodes on the other principal plane.
 9. A piezoelectric vibration device according to claim 8, wherein an area of the common electrode is formed to be larger than a total area of the input electrode and the output electrode, and the peripheral zone of the common electrode is at least partially provided with the weight reducing notch reaches the common electrode opposite to the input electrode and the output electrode.
 10. A piezoelectric vibration device according to claim 8, wherein the electrode formed on one principal plane of the quartz plate is thickly formed.
 11. A piezoelectric vibration device according to claim 8, wherein the common electrode formed on one principal plane of the quartz plate is twice to 10 times as thick as the input electrode and the output electrode formed on the other principal plane.
 12. A piezoelectric vibration device according to claim 8, wherein the each electrode is formed to be rectangular, and the weight reducing notch is disposed on one center of the far sides where the input electrode and the output electrode are opposite to each other as well as one center of the far sides opposite to the common electrode.
 13. A piezoelectric vibration device utilizing a thickness-shear vibration having resonant areas formed by two pairs of input and output electrodes and common electrodes, the piezoelectric vibration device comprising: a quartz plate having a pair of principal planes, the two pairs of input and output electrodes respectively including an input electrode and an output electrode, disposed on a principal plane of the quartz plate in parallel, in which the input electrode and the output electrode are formed close to each other at a regular interval, the common electrodes disposed on the other principal plane of the quartz plate, corresponding to the respective pairs of input and output electrodes, and a weight reducing notch disposed on each of peripheral zones of the input electrode, the output electrode, and the common electrode, and wherein the weight reducing notch is disposed on the peripheral zones where a vibrational energy of a spurious vibration, generated in excitation of the piezoelectric vibration device, is relatively greater than that of a principal vibration.
 14. A piezoelectric vibration device according to claim 13, wherein the weight reducing notch disposed on the electrodes on a principal plane reaches an area opposite and corresponding to the electrodes on the other principal plane.
 15. A piezoelectric vibration device according to claim 14, wherein an area of the common electrode is formed to be larger than a total area of the input electrode and the output electrode, and the peripheral zone of the common electrode is at least partially provided with the weight reducing notch reaches the common electrode opposite to the input electrode and the output electrode.
 16. A piezoelectric vibration device according to claim 14, wherein the electrode formed on one principal plane of the quartz plate is thickly formed.
 17. A piezoelectric vibration device according to claim 14, wherein the common electrode formed on one principal plane of the quartz plate is twice to 10 times as thick as the input electrode and the output electrode formed on the other principal plane.
 18. A piezoelectric vibration device according to claim 14, wherein the electrode formed on one principal plane of the quartz plate is made of gold, silver or a metal material mainly composed of gold or silver.
 19. A piezoelectric vibration device according to claim 1, wherein the weight reducing notch disposed on the electrodes on a principal plane reaches an area opposite and corresponding to the electrodes on the other principal plane.
 20. A piezoelectric vibration device according to claim 8, wherein the electrode formed on one principal plane of the quartz plate is made of gold, silver or a metal material mainly composed of gold or silver.
 21. A piezoelectric vibration device according to claim 14, wherein the each electrode is formed to be rectangular, and the weight reducing notch is disposed on one center of the far sides where the input electrode and the output electrode are opposite to each other as well as one center of the far sides opposite to the common electrode.
 22. A method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device, comprising the steps of: providing a quartz plate having a pair of principal planes, an input electrode and an output electrode on a principal plane of the quartz plate, the input electrode and the output electrode forming close to each other at a regular interval, and a common electrodes on the other principal plane of the quartz plate, corresponding to the input electrode and the output electrode, and notching peripheral zones of each of the input electrode, the output electrode, and the common electrode, to restrain a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device.
 23. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 22, wherein said notching step further comprises: notching on a portion where the vibrational energy of the spurious vibration, generated in excitation of the piezoelectric vibration device, is relatively greater than that of a principal vibration.
 24. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 22, wherein said providing step comprises providing: each electrode in the form of rectangular shape, and said notching step comprises notching on one center of the far side where the input electrode and the output electrode are opposite to each other as well as on one center of the far side opposite to the common electrode.
 25. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 22, wherein said providing step comprises providing: an area of the common electrode to be larger than a total area of the input electrode and the output electrode, and wherein said notching step comprises: notching the peripheral zone of the common electrode reaching the common electrode opposite the input electrode and output electrode.
 26. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 22, further comprising the steps of: said providing step comprises providing the common electrode on one principal plane of the quartz plate which is twice to 10 times as thick as the input electrode and the output electrode forming on the other principal plane.
 27. A method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device, comprising the steps of: providing a quartz plate having a pair of principal planes, an input electrode and an output electrode on a principal plane of the quartz plate, a grounding electrode interposed between the electrodes, in which the input electrode, the output electrode and the grounding electrode are respectively formed close to each other at regular intervals, and a common electrodes on the other principal plane of the quartz plate, corresponding to the input electrode, the output electrode, and the grounding electrode, and notching peripheral zones of each of the input electrode, the output electrode, and the common electrode, to restrain a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device.
 28. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 27, wherein said notching step further comprises: notching on a portion where the vibrational energy of the spurious vibration, generated in excitation of the piezoelectric vibration device, is relatively greater than that of a principal vibration.
 29. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 27, wherein said providing step comprises providing: each electrode in the form of rectangular shape, and said notching step comprises notching on one center of the far side where the input electrode and the output electrode are opposite to each other as well as on one center of the far side opposite to the common electrode.
 30. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 27, wherein said providing step comprises providing: an area of the common electrode to be larger than a total area of the input electrode and the output electrode, and wherein said notching step comprises: notching the peripheral zone of the common electrode reaching the common electrode opposite the input electrode and output electrode.
 31. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 22, further comprising the steps of: said providing step comprises providing the common electrode on one principal plane of the quartz plate which is twice to 10 times as thick as the input electrode and the output electrode forming on the other principal plane.
 32. A method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device, comprising the steps of: providing a quartz plate having a pair of principal planes, two pairs of input and output electrodes respectively including an input electrode and an output electrode, disposed on a principal plane of the quartz plate in parallel, in which the input electrode and the output electrode are formed close to each other at a regular interval, and a common electrodes on the other principal plane of the quartz plate, corresponding to the respective pairs of input and output electrodes, and notching peripheral zones of each of the input electrode, the output electrode, and the common electrode, to restrain a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device.
 33. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 27, wherein said notching step further comprises: notching on a portion where the vibrational energy of the spurious vibration, generated in excitation of the piezoelectric vibration device, is relatively greater than that of a principal vibration.
 34. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 27, wherein said providing step comprises providing: each electrode in the form of rectangular shape, and said notching step comprises notching on one center of the far side where the input electrode and the output electrode are opposite to each other as well as on one center of the far side opposite to the common electrode.
 35. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 27, wherein said providing step comprises providing: an area of the common electrode to be larger than a total area of the input electrode and the output electrode, and wherein said notching step comprises: notching the peripheral zone of the common electrode reaching the common electrode opposite the input electrode and output electrode.
 36. The method of restraining a vibrational energy of a spurious vibration generated in excitation of a piezoelectric vibration device of claim 22, further comprising the steps of: said providing step comprises providing the common electrode on one principal plane of the quartz plate which is twice to 10 times as thick as the input electrode and the output electrode forming on the other principal plane. 